A ruthenium aromatic ring complex as a ruthenium source having, as a ligand, a six-membered aromatic compound is used as a precursor for hydrogenation catalysts and complexes for hydrogen transfer. Further, in recent years, such a ruthenium aromatic ring complex has come to be used as a precursor for antitumor agents and thin film electrode materials for semiconductor devices, and therefore its demand is increasing.
A conventional method (i) for producing such a ruthenium aromatic ring complex is refluxing corresponding substituted 1,3- or 1,4-cyclohexadiene and ruthenium (III) trichloride trihydrate in ethanol or methanol (J. Chem. Soc., Dalton Trans (1974) p. 233).
Another conventional method (ii) for producing such a ruthenium aromatic ring complex is [RuCl2(p-cymene)]2 obtained by the method (i) and hexamethylbenzene or durene (1,2,4,5-tetramethylbenzene), which has a higher boiling point than p-cymene, were reacted at high temperature to exchange aromatic ring moieties (Inorg. Chem., 19(1980) p. 1014-1021 and Inorg. Synth., 21(1982) p. 74-78).